Tooth forming tool

ABSTRACT

A tool for pressure forming teeth on the periphery of a cylindrical workpiece, the tool having an improved tooth generating configuration which improves the useful life of the tools and which improves the flow characteristics of the metal in the workpiece during the tooth generating process.

United States Patent [191 Miller et al.

[11] 3,827,280 [451 Aug. 6, 1974 2,994,237 8/1961 Pelphrey 72/469 3,015,243 1/1962 Drader.....' 72/469 3,672,203 6/1972 Anderson 72/469 Primary Examiner-Milton S. Mehr Attorney, Agent, or Firm-Malcolm R. McKinnon [57] ABSTRACT A tool for pressure forming teeth on the periphery of a cylindrical workpiece, the tool having an improved tooth generating configuration which improves the useful life of the tools and which improves the flow characteristics of the metal in the workpiece during the tooth generating process.

8 Claims, 6 Drawing Figures 2% if; z; i V/ room FORMING TOOL BRIEF SUMMARY OF THE INVENTION This invention relates to tools for pressure forming toothed elements and, more particularly, to an improved tool for pressure forming teeth, such as spline teeth, gear teeth, worm teeth, serrations and the like, on the periphery of cylindrical workpieces while the workpieces are at ambient or room temperature and without removal of material from the workpieces. Heretofore, various tools have been utilized commercially to pressure from spline teeth, gear teeth, worm teeth, serrations and the like on the periphery of a cylindrical workpiece while the workpiece is at ambient or room temperature without removing material from the workpiece. Examples of prior art tools which have achieved commercial success in this field are disclosed in US. Pat. Nos. 2,994,237 and 3,015,243, such tools being utilized in machines of the type disclosed in US. Pat. No. 2,995,964.

An object of the present invention is to provide an improved tooth forming tool of the indicated character incorporating improved means for generating teeth on toothed elements whereby the strength and useful life of such tools is increased.

Another object of the invention is to provide an improved tool for pressure forming toothed elements which enables the quantity production of toothed elements with improved quality.

Another object of the invention is to provide an improved tooth forrning tool incorporating improved tooth generating means which improves the flow characteristics of the metal in the workpiece during the tooth generating process.

Still another object of the invention is to provide an improved tool for pressure forming toothed elements which tool is economical and commercially feasible to manufacture, durable, efficient and reliable in operatron.

The above as well as other objects and advantages of the present invention will become apparent from the following description, the appended claims and the ac companying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevational view of a pair of rack type tools embodying the present invention, showing the same installed in schematically illustrated apparatus for utilizing such tools;

FIG. 2 is a side elevational view of the entire bottom rack type tool illustrated in FIG. 1;

FIG. 3 is a fragmentary view of a typical involute spline that can be pressure formed by tools embodying the present invention;

FIG. 4 is an enlarged, fragmentary and diagrammatic side elevational view of the teeth of the tools illustrated in FIGS. 1 and 2;

FIG. 5 is an elevational view of the left end of the tool illustrated in FIG. 2, and

FIG. 6 is a fragmentary, top plan view of the tool il- Iustrated in FIG. 2.

DETAILED DESCRIPTION Referring to the drawings, a preferred embodiment of the invention is illustrated in FIGS. 1, 2, 4, 5 and 6 thereof. The illustrated embodiment of the invention comprises a specific tooth construction for each of a pair of identical rack type tools, generally designated 10A and 10B, which may be utilized to pressure form involute spline teeth or involute gear teeth as well as other types of teeth on the periphery of a cylindrical workpiece. A machine in which a pair of rack type tools embodying the present invention may be utilized to pressure form a workpiece by metal displacement is described in detail in the aforementioned US. Pat. No. 2,995,964 although it will be understood that tools embodying the present invention may be utilized in other types of machines. In general, as illustrated in FIG. 1, a workpiece 12 is positioned between the lower and upper tools 10A and 10B embodying the present invention, the tools 10A and 108 being shown at the beginning of the operation which will pressure form teeth on the periphery of the workpiece 12. The workpiece I2 is preferably supported by means (not shown) which permit it to rotate freely about the longitudinal axis of the workpiece when urged to do so by the tools 10A and 108.

The lower and upper tools 10A and 10B are illustrated as identical rack type tools with teeth on their opposing faces that engage the periphery of the workpiece 12. The tools are movable lengthwise by suitable means and are illustrated as being slidable on ways 14 and 16 that are formed in the bed 18 and head 20, respectively, of the machine which carries the tools. Means are provided to simultaneously move the tools 10A and 108 in opposite directions. Such means is schematically illustrated as a pair of identical pressure cylinders 22 and 24 having pressure ports 26 and 28 at one end and pressure ports 30 and 32 at the opposits end. Working in these cylinders are pistons 34 and 36 having rods 38 and 40, respectively. The rod 38 is affixed to the trailing end of the tool 10A and the rod 40 is affixed to the trailing end of the tool 10B. Suitable valving and synchronizing mechanisms (not shown) can be used with the cylinders 22 and 24 to actuate and synchronize their operation so that the tools 10A and 10B move at the same instant and with the same velocities in opposite directions as more fully described in US. Pat. No. 2,995,964.

The operation of the apparatus is evident from the above description. With the tools 10A and 10B mounted in the position shown and with the workpiece 12 supported by means which permit it to rotate freely about its longitudinal axis when urged to do so by the tools 10A and 108, the piston and cylinder units 22 and 24 are actuated so as to move the tools 10A and 10B simultaneously and at the same velocity in opposite directions past the workpiece 12. The spacing between the working faces 42 and 44 of the tools 10A and 10B is less than the diameter of the workpiece 12 with the result that the configuration of the faces 42 and 44 is impressed or conjugated on the periphery of the workpiece. The end of the stroke is reached when the trailing ends 46 and 48 of the tools pass over the workpiece 12 at which point the workpiece 12 may be removed and the tools 10A and 10B returned to the starting positions illustrated in FIG. I wherein the leading ends 50 and 52 are adjacent the workpiece 12. A new workpiece can then be inserted in the apparatus and the operation repeated.

In forming teeth of the desired configuration on the periphery of the workpiece 12, the material from which the workpiece is made (ordinarily steel) will flow adjacent the surface in radial and tangential directions so that there are grooves of less than the original diameter of the workpiece and ridges of greater than the original diameter of the workpiece. Since the final configuration of the workpiece usually must be accurately maintained, this flow of material should be taken into account in selecting the diameter of that portion of the workpiece 12 which is subjected to the action of the tools A and 108.

To illustrate by consideration of a common but very important shape that may be rolled by tools embodying the present invention, there is shown in FIG. 3 a portion of a cross-section of a workpiece 12 in finished form in which the workpiece has involute teeth or splines 54. Since no metal is removed in the cold rolling operation, the diameter of the workpiece prior to rolling cannot be either the final outside diameter or the root diameter. The rolling diameter D of the workpiece 12 is selected so that the area 56 of removed tooth material below the D periphery is equal to the area 58 of tooth material on a greater diameter than D The diameter D,, or substantially this diameter, defines the pitch line for rack type tools such as the tools 10A and 108. As will be described hereinafter in greater detail, the pressure angle or obliquity of certain of the teeth of the tools 10A and 10B is the angle whose cosine is D/D multiplied by the cosine of the pressure angle at the pitch diameter of the teeth 54 where D is the pitch diameter of the workpiece 12. The base pitch of the tools and the workpiece are identical. With such a construction, the linear pitch of the teeth on the tool, as measured on the pitch line thereof, corresponds with the circular pitch of the teeth on the workpiece, as measured on a circle having the diameter D of the workpiece. The whole depth of at least some of the teeth on the tools 10A and 108 which engage the workpiece 12 is preferably the same as that of the work piece, i.e., such tool teeth are fully conjugate to the teeth on the workpiece.

The tools 10A and 10B are spaced apart so that at a position near the trailing ends thereof, the working faces 42 and 44 provide a clearance equal to the root diameter of the workpiece 12 less a few thousandths of an inch to take up elasticity of the members and compression of oil films under rolling pressure. Only one pass of the tools with no reversal of direction during the working stroke is preferred.

The spacing of the working faces 42 and 44 of the tools 10A and 10B is regulated so that the depth of the impressions made in the workpiece gradually increases as the rolling operation proceeds. That is to say the faces 42 and 44 approach closer together toward the longitudinal axis of the workpiece as the length of the stroke increases. This approach may be regarded as the feed of the tools into the workpiece as the tools move relative to the workpiece. In the embodiment of the invention illustrated, the convergence of the tool faces toward each other is accomplished by gradually increasing the height of successive sections of the tool teeth while maintaining the pitch line of all sections of the tool teeth from the leading end of the tool to the section containing the fully conjugate teeth constant, a divergent section of the teeth being provided between the section containing the fully conjugate teeth and the trailing end of the tool to provide relief at the end of the working stroke of the tool.

2, 4, 5 and 6 illustrate a bottom tool 10A embodying the present invention, it being understood that the tooth formation of the upper tool 108 will be subsantially identical. The numeral designates a theoretical reference line which shows a no taper condition. If the lower and upper ways 14 and 16 may be considered as being disposed in parallel planes, the line 60 may be considered as being parallel to the ways 14 and 16 so that if the tops of the teeth on the tool remained on the line 60 there would be no change in spacing between the faces 42 and 44 as the tools moved on the ways 14 and 16. The teeth of the tool 10A are designated generally by the numeral 62 and, in the preferred embodiment of the invention illustrated, the teeth 62 are divided into seven sections delineated by the vertical reference lines 64, 66, 68, 70, 72 and 74 and the trailing and leading ends 46 and 50, respectively, of the tool. As shown in FIG. 4, the pitch line 76 of the tool teeth 62 is parallel to the reference line 60 from the leading end 50 of the tool 10A to the reference line 64, and the pitch line of the tool teeth 62 tapers downwardly away from the reference line 60 from the reference line 64 to the trailing end 46 of the tool. The tops of the tool teeth in the sections between the reference line 64 and the leading end 50 of the tool are stepped downwardly in successive sections toward the leading end of the tool while the pitch line of the teeth in the sections of teeth between the reference line 64 and the leading end 50 of the tool remains parallel to the reference line 60.

In accordance with the teaching of U.S. Pat. No. 3,015,243, the teeth 62A between the reference lines 64 and 66 are full sized and fully conjugate to the teeth to be formed on the workpiece and the pressure angle or angle of obliquity of the teeth 62A is the angle whose cosine is D/D multiplied by the cosine of the pressure angle at the pitch diameter of the teeth to be formed on the workpiece where D is the pitch diameter of the teeth of the workpiece. The teeth 62A between the reference lines 64 and 66 conjugate the final form of the teeth on the workpiece. Also, in accordance with the teachings of U.S. Pat. No. 3,015,243, and as previously mentioned, the pitch line of the teeth 628 between the reference line 64 and the trailing end 46 of the rack tapers downwardly away from the reference line 60 and the teeth 628 between the reference line 64 and the trailing end 46, while being substantially full-sized, are also relieved on the sides or flank faces thereof. This relief eliminates seam lines and other errors that might otherwise be formed on the teeth of the workpiece at the end of the stroke due to the decreased total area of the contact between the tools and the workpiece as the rolling pressures are reduced at the end of the stroke.

In accordance with the present invention, the pitch line of all of the teeth on the tool between the reference line 64 and the leading end 50 of the tool is determined by the diameter D of the workpiece in the manner previously described so that the linear pitch of the teeth on the tool, as measured on the pitch line thereof, corresponds with the circular pitch of the teeth on the workpiece as measured on a circle having the diameter D of the workpiece. As previously mentioned, the pressure angle of the full-sized teeth 62A between the reference lines 64 and 66 is the angle whose cosine is D/D multiplied by the cosine of the pressure angle at the pitch diameter of the teeth on the workpiece where D is the conventional pitch diameter of the workpiece.

The base pitch of the tools and the workpiece is identical. With such a construction, the linear pitch of the teeth on the tool, as measured on the pitch line thereof, corresponds with the circular pitch of the teeth on the workpiece as measured on a circle having the diameter D, of the workpiece. The whole depth of the teeth 62A between the reference lines 64 and 66 is preferably the same as that of the workpiece so that the teeth 62A are fully conjugate to the teeth on the workpiece.

Between the leading end 50 of the tool and the reference line 74, the tool working surface is provided with sharp file-like teeth 62C which initially grip the workpiece and initiate its rotation. In use, the teeth 62C in the upper and lower tools are spaced apart by a distance slightly less than the rolling diameter D of the workpiece, as for example, the teeth 62C of the upper and lower tools may be spaced apart a few thousandths of an inch less than the diameter D of the workpiece.

The linear pitch of the teeth 62C is identical with the linear pitch of the teeth in all other sections of the rack. The number of teeth 62C is preferably one-half the number of teeth in the workpiece, i.e. if there are 20 teeth in the workpiece, there will be teeth 62C in the section of the tool between the reference line 74 and the leading end 50 of the tool.

It will be noted that the reference line 60 is tangent to the tops of the full-sized teeth 62A in the section of the teeth on the tool between the reference lines 64 and 66. The reference line 78 is parallel to the reference line 60 and is tangent to the roots of the teeth 62A between the reference lines 64 and 66. In accordance with the present invention, in the section of the tool teeth between the reference lines 66 and 68, the addenda of all of the teeth 62D are ground off so that the tips of the teeth 62D are disposed below the tips of the full-sized teeth 62A in the section of the teeth between the reference lines 64 and 66. At the same time, the flanks of the teeth 62D are relieved slightly so that the thickness of the teeth 62D as measured on the pitch line is slightly less than the thickness of the full-sized teeth 62A, as measured on the pitch line.

In accordance with the teachings of U.S. Pat. No. 2,994,237, at the junction of the leading and trailing flanks of the teeth 62A with the tops thereof, the teeth 62A are provided with a predetermined radius MA, as for example a radius of 0.016 inch. In accordance with the present invention, at the junction of the leading and trailing flanks of the teeth 62D with the tops thereof, the teeth 62D are provided with a radius 80D which is slightly'greater than the radius 80A provided at the juncture of the leading and trailing flanks of the teeth 62A with the tops thereof. For example, the radius 60D may be 0.020 inch. As shown in FIG. 4, the root line of the teeth 62D is also disposed above the root line of the teeth 62A so that the teeth 62D have a slightly modified addenda and a slightly modified dedenda as compared with the full-sized teeth 62A. For example, if the thickness of the teeth 62A, as measured on the pitch line thereof is 0.0722 inch, the thickness of the teeth 62D as measured on the pitch line thereof may be 0.0682 inch, and if the total height of the teeth 62A is 0.083 inch, the total height of the teeth 62D may be 0.077 inch.

Also in accordance with the present invention, the tips of the addenda and roots of the dedenda of the teeth 62E, 62F and 626 in the sections between the reference lines 68-70; 70-72, and 72-74, respectively, are defined by radii, the radius F defining the tips of the addenda of the teeth 62F being greater than the radius 80E defining the tips of the addenda of the teeth 62E, and the radius 82F defining the roots of the dedenda of the teeth 62F being greater than the radius 62E defining the roots of the dedenda of the teeth 62E. The radius 80G defining the tips of the addenda of the teeth 626 is also greater than the radius 80F defining the tips of the addenda of the teeth 62F and the radius 826 defining the roots of the dedenda of the teeth 62G is greater than the radius 82F defining the roots of the dedenda of the teeth 62F. By way of example, the tips of the addenda of the teeth 62E may be formed on a radius of 0.036 inch while the roots of the dedenda of the teeth 62E may be defined by a radius of 0.038 inch. The addenda of the teeth 62F may be defined by a radius of 0.044 inch and the dedenda of the teeth 62F defined by a radius of 0.044 inch. The addenda of the teeth 626 may be defined by a radius of 0.048 inch and the dedenda of the teeth 62G defined by a radius of 0.056 inch. Also, as shown in FIG. 4, the tips of the teeth 62E are disposed below the tips of the teeth 62D, and the tips of the teeth 62F and disposed below the tips of the teeth 62E. The tips of the teeth 626 are also disposed below the tips of the teeth 62F. At the same time, the root lines of the teeth 62D, 62E, 62F and 626 are disposed above the root lines of the teeth in the preceding sections of teeth progressing toward the full sized teeth 62A. The chordal thickness of the teeth 62E, 62F and 62G, as measured on the pitch line thereof, also progressively increases progressing from the teeth 62G toward the full-sized teeth 62A while the distance between the teeth of successive sections, as measured on the pitch line, progressively decreases progressing from the teeth 62G toward the teeth 62A.

Thus, it will be seen that the tips of the addenda of the tool teeth 62G, 62F and 62B in each successive section of teeth are defined by radii, which radii progressively decrease in each section progressing from the teeth 62G toward the full heightteeth 62A. The roots of the dedenda of the teeth in each successive section are also defined by radii, which radii progressively decrease in each section of teeth progressing from the teeth 62G toward the full height teeth 62A. At the same time, the root lines of the teeth in each successive section are progressively lowered from the leading end 50 of the tool to the full height teeth 62A while the tip lines of the teeth in each successive section are progressively raised from the leading end 50 to the tip line of the full height teeth 62A. The thickness of the various sections of the teeth, as measured! at the pitch line, progressively increases from section to section from the leading end 50 to the section containing the full-size teeth 62A while the distance between the teeth in the various sections, as measured on the pitch line thereof,

progressively decreases from the leading end 50 to the section containing the full height teeth 62A. With such a construction, the sharp teeth 62C initially engage and penetrate the workpiece slightly to initiate rotation thereof. The teeth 62G, 62F and 62E then successively engage the workpiece and generate a generally cycloidal tooth configuration, which generally cycloidal configuration is then gradually modified by the teeth 62D to a generally involute configuration after which the teeth 62A generate a true involute tooth configuration in the workpiece. It will be noted that the teeth between sections are blended, as illustrated at 84 in FIG. 4, so as to provide a smooth transition between the various sections of teeth in the tool.

If desired, one or both of the top corners of the tool 10A may be provided with a chamfer as shown in FIG. 5, or a radius, to eliminate the necessity of undercutting the workpiece. FIG. 6 illustrates a plan view of the teeth 62 when such teeth are intended to generate spur teeth on the workpiece. It will be seen that the tool teeth are perpendicular to the sides of the tool, i.e. perpendicular to the direction of tool movement. It will be understood that if the tools are to generate helical teeth on the workpiece, the tool teeth will be inclined to the sides of the tool or direction of tool movement.

While a preferred embodiment of the invention has been illustrated and described, it will be understood that various changes and modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A tool for pressure forming teeth on the periphery of a cylindrical workpiece, said tool including a body having a leading end and a trailing end and provided with a working face having a plurality of teeth thereon, a first section of said teeth being disposed between said leading end and said trailing end, each of said teeth in said first section having a configuration conjugate to the configuration of the teeth to be formed on the workpiece and having a pitch line, second, third and fourth sections of teeth being disposed between said leading end and said first section of teeth, the tips and roots of the teeth in said second, third and fourth sections being defined by radii, the radius defining the tips of the teeth in said third section being greater than the radius defining the tips of the teeth in said second section and the radius defining the tips of the teeth in said fourth section being greater than the radius defining the tips of the teeth in said third section.

2. A tool as set forth in claim 1 wherein the radius defining the roots of the teeth in said third section is greater than the radius defining the roots of the teeth in said second section and the radius defining the roots of the teeth in said fourth section is greater than the radius defining the roots of the teeth in said third section.

3. A tool as set forth in claim 1 wherein the tips of the teeth in said second section are disposed below the tips of the teeth in said first section, the tips of the teeth in said third section are disposed below the tips of the teeth in said second section and the tips of the teeth in said fourth section are disposed below the tips of the teeth in said third section.

4. A tool as set forth in claim 1 wherein the root line of the teeth in said second section is disposed above the root line of the teeth in said first section, the root line of the teeth in said third section is disposed above the root line of the teeth in said second section and the root line of the teeth in said fourth section is disposed above the root line of the teeth in said third section.

5. A tool as set forth in claim 1 wherein the chordal thickness of the teeth in said sections as measured on the pitch line thereof progressively decreases from section to section from the teeth in said first section to said leading end.

6. A tool as set forth in claim 1 wherein all of said teeth have a common pitch line.

7. A tool as set forth in claim 1 wherein the distance between the teeth of successive sections as measured on the pitch line thereon progressively decreases progressing from said leading end to said first section of teeth.

8. A tool as set forth in claim 1 including a fifth section of teeth adjacent said leading end, the tips of the teeth in said fifth section being sharp, the linear pitch of all of the teeth in all of said sections being constant. l 

1. A tool for pressure forming teeth on the periphery of a cylindrical workpiece, said tool including a body having a leading end and a trailing end and provided with a working face having a plurality of teeth thereon, a first section of said teeth being disposed between said leading end and said trailing end, each of said teeth in said first section having a configuration conjugate to the configuration of the teeth to be formed on the workpiece and having a pitch line, second, third and fourth sections of teeth being disposed between said leading end and said first section of teeth, the tips and roots of the teeth in said second, third and fourth sections being defined by radii, the radius defining the tips of the teeth in said third section being greater than the radius defining the tips of the teeth in said second section and the radius defining the tips of the teeth in said fourth section being greater than the radius defining the tips of the teeth in said third section.
 2. A tool as set forth in claim 1 wHerein the radius defining the roots of the teeth in said third section is greater than the radius defining the roots of the teeth in said second section and the radius defining the roots of the teeth in said fourth section is greater than the radius defining the roots of the teeth in said third section.
 3. A tool as set forth in claim 1 wherein the tips of the teeth in said second section are disposed below the tips of the teeth in said first section, the tips of the teeth in said third section are disposed below the tips of the teeth in said second section and the tips of the teeth in said fourth section are disposed below the tips of the teeth in said third section.
 4. A tool as set forth in claim 1 wherein the root line of the teeth in said second section is disposed above the root line of the teeth in said first section, the root line of the teeth in said third section is disposed above the root line of the teeth in said second section and the root line of the teeth in said fourth section is disposed above the root line of the teeth in said third section.
 5. A tool as set forth in claim 1 wherein the chordal thickness of the teeth in said sections as measured on the pitch line thereof progressively decreases from section to section from the teeth in said first section to said leading end.
 6. A tool as set forth in claim 1 wherein all of said teeth have a common pitch line.
 7. A tool as set forth in claim 1 wherein the distance between the teeth of successive sections as measured on the pitch line thereon progressively decreases progressing from said leading end to said first section of teeth.
 8. A tool as set forth in claim 1 including a fifth section of teeth adjacent said leading end, the tips of the teeth in said fifth section being sharp, the linear pitch of all of the teeth in all of said sections being constant. 